Field of the Invention
The invention relates to a method for driving a printing press, particularly a sheet-fed press having an integrated device for producing a printing form, and a device for performing the method.
Printing presses have become known heretofore wherein laser imaging heads are allocated to printing-form cylinders with which ink-accepting pixels or half-tone dots are generated on a printing plate or a printing form within the printing press. A variety of disruptions or disturbances act upon the imaging process, influencing the position of the pixels or half-tone dots on the printing plate or printing form. The printing-form cylinder is rotated during the imaging process, it being possible to gather or record the entire surface by guiding an imaging head parallel to the axis of rotation of the printing-form cylinder. The slightest mechanical vibrations and impacts acting upon the system of the printing-form cylinder and the imaging head cause imaging errors that cannot be corrected without further ado.
The published German Patent Document DE 692 22 035 T2 teaches a method whereby unroundnesses of a printing-form cylinder are corrected by controlling the time of an imaging process, pixel by pixel. The published German Patent Document DE 692 22 801 T2 describes an improvement wherein a correction value is assigned to each pixel to be set. Therewith, corrections can be made in both the circumferential and lateral directions of a printing-form cylinder. It is possible to compensate for periodic and predictable disturbance variables with such software-based methods. Disturbances due to high-frequency vibrations and impacts can be only inadequately compensated for due to the limited signal processing speed of a computer.
The published German Patent Document DE 197 23 147 A1 teaches a method for driving a printing press having an integrated imaging device whereby the drive of the printing-form cylinder is decoupled from the drive train, the printing-form cylinder is driven by a separate drive in the imaging operation, and following the imaging operation, the drive of the printing-form cylinder is reintegrated into the drive train in the operating-phase position. By decoupling the printing-form cylinder, influences of the drive train upon the imaging process are avoided. Because of the required clutch, this construction is quite expensive.
The published German Patent Document DE 198 22 893 A1 teaches a construction whereby all non-uniformly rotating subassemblies of a printing press are decoupled from the printing-form cylinder drive, and all uniformly rotating subassemblies are driven together with the printing-form cylinder. Besides one or more clutches, powerful motors are needed for the drive of the printing-form cylinder and the uniformly moving groups.
To prevent printing disturbances, the published German Patent Document DE 196 23 224 C1 describes a drive for a sheet-fed press wherein printing-unit cylinders can be driven while mechanically decoupled from the gear train of a sheet transfer system. By the separate driving of a plate cylinder, for example, the effects of load fluctuations in the gear train of the sheet transfer system on the plate cylinder during the printing operation are prevented. The separate driving of a plate cylinder additionally permits the correction of the circumferential register and the print length and an improvement in the flexibility, because plate exchange and washing processes can occur in unoccupied printing units during the printing operation. The angular synchronicity between plate cylinders and the sheet transfer system must be realized by an intensive or expensive control.
It is accordingly an object of the invention to provide a method and a device for driving a printing press wherein a driving concept for a printing press with an integrated imaging device is developed which permits both the printing operation and a faultless imaging operation, with little outlay.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for driving a printing press, which comprises driving, in a printing operation, via a gear train by at least a first motor, at least one drum for advancing printing material and a printing-form cylinder; processing angle-of-rotation signals of the drum in a control device for controlling the driving of the drum and the form cylinder; driving, in a printing-form production operation in the printing press, a printing-form cylinder by a separate motor; and in an operation for producing the printing form, synchronously actuating the first motor and the separate motor by providing a gear allocated to the driving of the printing-form cylinder, and an adjacent gear allocated to the driving of the drum of the gear train, the gears being disposed relative to one another at most out of contact with one another, and at least barely in engagement with one another so as to exert a slight pressure on one another.
In accordance with another mode, the method of the invention further comprises, during the printing-form production operation, processing, in the control device, signals indicating the angle of rotation of the printing-form cylinder.
In accordance with a concomitant aspect of the invention, there is provided a printing press comprising a gear train for driving a printing-form cylinder and at least one drum for advancing printing material; at least one first motor for driving the printing press during a printing operation and an additional motor for driving the printing-form cylinder during a production of a printing form in the printing press; a rotary position transducer for detecting an angular position of the printing-form cylinder and the drum, respectively, during the printing operation; a motor control device connected to the rotary position transducer; and an additional rotary position transducer connected to the motor control device for detecting an angular position of the printing-form cylinder during the production of the printing form.
The invention is based on the concept that, by a control device for a printing press drive, a motor for driving a printing-form cylinder is so actuated relative to a main drive train of the press in an imaging operation that no contact of tooth sides or flanks occurs between the gears driving the printing-form cylinder and those powering the main drive train. Thus, no torsional vibrations are transferred to the main printing-form cylinder from the main drive train. This improves the quality of the imaging of the printing-form cylinder.
Applying the method of the invention, a printing press can be constructed so that, during a printing operation, it is driven by one or more motors that are coupled to the main drive train. The separate motor for driving the printing-form cylinder can be deactivated during the printing operation or can act as an auxiliary drive to secure the contact of the tooth sides or flanks and/or to prevent printing disturbances or errors. In the imaging operation, both motors are controlled by one control device. In contrast with the printing operation, in order to prevent a transfer of vibrations to the printing-form cylinder, the tooth-side or tooth-flank contact between two gears, which are allocated to the main drive train and the secondary drive train for driving the printing-form cylinder, respectively, is prevented. The main drive train and the secondary drive train are advantageously driven so that the gears which are allocated to the transfer cylinder and the printing-form cylinder do not contact one another. It is advantageous, when signals are transmitted by a rotary position transducer for indicating the angle of rotation and the torsional vibrations of the transfer cylinder, and processed in the control device. Clutches for separating from the main drive train and the secondary drive train can be dispensed with. Because the gear train in the printing press does not have to be disengaged, assurance is provided that the angular position will not be shifted by clutch-engagement and clutch-disengagement operations.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a device for driving a printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: